1. Field of the Invention
This invention relates to an object locating or tracking system or process in which a vector field which is caused to nutate about an axis called the pointing vector, is used to locate or track a remote object. It also relates to an apparatus for generating such a nutating field, more particularly a nutating magnetic field, which nutates about an axis called the pointing vector. More particularly, the invention relates to such a system or process wich is capable of determining both the relative translation and the relative angular orientation of the coordinate frame of a remote object, relative to the reference coordinate frame of the apparatus which generates and points the nutating field.
II. Description of the Prior Art
The use of orthogonal coils for generating and sensing magnetic fields is well known. Such apparatus has received wide attention in the area of mapping magnetic fields to provide a better understanding of their characteristics, for example. If a magnetic field around generating coils can be very accurately mapped through use of sensing coils, it has also been perceived that it might be possible to determine the location of the sensing coils relative to the generating coils based on what is sensed. However, a problem associated with doing this is that there is more than one location and/or orientation within a dual magnetic dipole field that will provide the same characteristic sensing signals in a sensing coil. In order to use a magnetic field for this purpose, additional information must therefore be provided.
One approach to provide the additional information required for this purpose is to have the generating and sensing coils move with respect to each other, such as is taught in U.S. Pat. No. 3,644,825. The motion of the coils generates changes in the magnetic field, and the resulting signals then may be used to determine direction of the movement or the relative position of the generating and sensing coils. While such an approach removes some ambiguity about the position on the basis of the field sensed, its accuracy is dependent on the relative motion, and it cannot be used at all without the relative motion.
Another approach that has been suggested to provide the additional required information is to make the magnetic field rotate as taught in Kalmus, "A New Guiding and Tracking System", IRE Transactions on Aerospace and Navigational Electronics, March 1962, pages 7 - 10. To determine the distance between a generating and a sensing coil accurately, that approach requires that the relative orientation of the coils be maintained constant. It therefore cannot be used to determine both the relative translation and relative orientation of the generating and sensing coils.
While the art of locating and tracking remote objects is a well developed one, there still remains a need for a way to determine the relative angular orientation of a remote object in addition to locating or tracking the object. Further, there is a need for a means, system or process which operates on the signals detected by one sensor, those signals resulting from the nutating field generated by one generating means, which is capable of determining continuously the location of or tracking the remote object and sensor, in addition to simultaneously determining continuously the relative angular orientation of the remote object and sensor.